Treatment of malleable castings



Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE IRVING R. VALENTINE, OF ERIE, PENNSYLVANIA, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK rnm'rmnnr or MALLEABLE CASTINGS No Drawing.

My present invention relates to malleable cast iron, and more particularly to the heat treatment of malleable castings;

In my copending application, Serial No. 7 5,665, filed December 19, 1925, and of which the present application is a continuation in part, there is disclosed a method for treating malleable castings whereby embrittlement of the castings during the galvanizing process is prevented. Such castings, however, in actual practice are frequently exposed to varying weather conditions and are, therefore, subjected to wide changes in temperature, and I have found that under certain conditions as where castings are subjected to temperatures well below 0 C., brittleness may sometimes occur after the castings have been galvanized, even though no brittleness developed during the galvanizing process itself.

It is one of the objects of my invention to provide a method of treating malleable castings whereby such castings are rendered free from embrittlement not only during, but subsequent to the galvanizing process.

It is a further object of my invention to provide means for restoring either black or galvanized malleable castings, which havebecome embrittled, to a normal or unembrit tled condition. I. f

According to the present invention, I heat malleable castings to a temperature which is within the range of 100 C. and 540C. and age the castings at this temperature for a period of time varying from 3 to 7 2 hours, the ageing period and temperature employed varying according to the condition of the casting. Copper coated galvanized castings treated in this manner are rendered immune from embrittlement when submitted to-cold tests subsequent to the galvanizing process, while castings which have been rendered brittle either in. the galvanizing process or by other meansare restored to normal, unembrittled condition.

In carrying out my invention malleable castings are galvanized substantially in-the manner described in my prior application 4 above referred to. The malleable castings are first cleaned by placing them in an acid Application filed May 20,

1926. Serial No. 110,546.

solution. Although a sand blast might be employed for this purpose, I have found that the latter method of cleaning iron is generally unsatisfactory since there is a tendency to leave a small thin film of sand on the metal which 1s detrimental to the process employed. After the iron has been removed from the acid solution, it is provided with a relatively thin copper coating which is obtained by dipping the iron momentarily in a copper sulphate solution to which a mercury salt and concentrated sulphuric acidhave been added,

.and which may advantageously be kept in an-agitated condition by means of any suitable stirring device.

The proportions of materials employed in the solution are substantially as follows:

Water W 1 gallon. Copper sulphate 2.5 pounds. Mercurous nitrate 1 oz.. Concentrated sulphuric acid l pound. These figures represent approximate amounts only and may vary within certain limits both above and below the figures given. Although the use of copper sulphate and mercurous nitrate gives very satisfactory results, other copper salts may be substituted for the sulphate if desired, and practically any mercury salt may be substituted for the mercurous nitrate. While a relatively small amount of mercury salt will usually be employed, larger amounts may be used Without causing any deleterious effect, since the mercury which adheres to the iron will be distilled in the presence of the molten zinc.

For the successful galvanizing of malleable castings, according to the method dis closed in my prior application, it is necessary that the copper form an adherent coating on the malleable iron. I have found that, by employing a mercury salt in the copper solution such a coating may be obtained; that the appearance of the copper deposit is thereby improved and that it cannot ordinarily be rubbed off.

After the malleable iron is dipped in the copper sulphate solution, it is rinsed in water or alcohol and dried by heating to a temperaperature between 120 C. and 145 G. for a period of approximately 6hours, after which the castings are removed and cooled in the air. Although I find a temperature range from 120 C. to 145 C. to be most suitable for carrying my invention into effect, this temperature range may be varied considerably. In general, however, the temperature employed will not be lower than 100 0. nor higher than 165 C., since above the latter temperature the zinc coating has a tendency to peel. Likewise, althoughthe most suitable period for ageing will be found to be approximately 6 hours, this period may be considerably longer. Good results may furthermore be obtained by ageing the castings for as'short a period as three hours, although in the latter case, it will be found advisable to cool the castings quickly at the end of the ageing period, as by'immersing in water,

, rather than to cool them in air. I have found from numerous tests that malleable iron castings which have been galvanized and heat treated, as above described, are not only free from embrittlement during the .galvanizing process, but that they will not subsequently become embrittled even when subjected to relatively low temperatures.

If desirel, a similar heat treatment may be applied to malleable castings which have received no treatment, such as a copper coating, prior to galvanizing. In this case, however, it will usually be found advisable to age the castings at an elevated temperature for a longer period of time than when the castings are copper coated, although otherwise the process is the same. For example, ordinary malleable castings may be galvanized in the usual maner, by applying to the casting. molten zinc having a temperature of approximately 450 C. The castings are then quenched in warm water of approximately 80 C. and thereafter aged in a heated compartment, at a temperature which may range from 120 C. to 145 C., and for approximately 36 hours, after which the castings are removed and cooled in the air. Although the average ageing period of 36 hours will be found satisfactory, this period may vary considerably, but usually will not be less than-6 hours or more than 7 2 hours in duration.- Likewise, although 120 C. to 145 0. indicates the most desirable range of temperature to be employed in the ageing process, this range may be extended both carried out in a furnace, care should beta en to protect the casting from free flames or fromthe action of the products of combustion. Although the application of molten zinc to malleable castings will ordinarily cause embrittlement of. the castings, I have found that when the castings are submitted to the heat treatment indicated above, the galvanized castings are free from embrittlement, and the zinc coating is uninjured.

Malle'ablc castings are frequently rendered extremely brittle from other causes than galvanizing, and I have found-from numerous tests that this extreme brittleness may be removed by heating the castings toa temperature which, as a rule, will be in excess of that employed in connection with this heat treatment of galvanized castings, and by then ageing the castings for a perlod of time varying from 6 to 72 hours.

WVhile it has previously been suggested that brittle malleable castings may be restored by heating to an elevated temperature such as 675 C. and then quenching, the apparatus employed in connection with such high temperature treatment is necessarilyexpensive and complicated, and it has been my experience that such heat treatment does not uniformly restore brittle castings to normal condition, due possibly to variation in the composition of the castings.

According to the present invention, malleable castings which have become embrittled are heated to a temperature of approximately 300 (1., maintained or aged at this temperature for a period of approximately 36 hours and then cooled in air. While both the temperature and the ageing period given are indicative of the best mode of carrying my invention into effect they may vary to a considerable extent. In general. the temperature employed will not be less than 100 C. nor over 540 C. and the ageing period will range from 6 to 72 hours in duration, the lower ageing period being usually associated with the higher temperature and vice versa. Brittle castings treated in this manner are restored to normal condition and show uniformly a complete absence of brittleness, even after having beensubjected to very low temperature tests. Of course, castings which have become brittle by galvanizing could be restored by heating to approximately 300 C. and ageing. This temperature, however, would destroy the zinc coating and necessitate further galvanizing.

Although I am at the present time not preing at an elevated temperature to the casting,

pared to give a theoretical explanation of the action that takes place in malleable castings when they are aged for prolonged periods at temperatures above 100 C. but below 540 C., I have nevertheless demonstrated by a great number of tests that by such a treatment copper coated castings are rendered immune from subsequent embrittlement and that brittle malleable castings are restored to a nor mal unembrittled condition.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of treating zinc coated malleable cast iron which comprises ageing the casting at a temperature above 100 C. but belowa temperature at which the zinc coating will peel.

2. The method of treating zinc coated malleable cast iron which comprises ageing the casting for at least three hours at a temper-' ature within the range of 100 C. to 165 C. 3. The method of treating malleable cast iron which comprises applying a zinc coatquenching the casting, and ageing the casting at a temperature above 100 C. but lower than the temperature at which the zinc coating will peel.

'4. The method of treating malleable cast iron which comprises applying a copper coating to the casting, superimposing a zinc coating on the said copper coating, and ageing the casting at a temperature above 100 C but lower than the temperature at which the zinc coating will peel. v I

5. The method of treatin malleable cast iron which comprises providing the casting with a copper coating, applying molten zinc to the copper coating, quenching the castin and ageing it at a temperature above 100 but not in; excess of 165 C.

6. The method of treating malleable cast iron which comprises applying a copper solution to the casting to provide acopper coating thereon, applying molten zinc to the copper coating, quenching the casting, ageing the casting at an elevated temperature not in excess of 165 C. and air cooling.

7. The method of-treating malleable cast iron which comprises applying to the casting a copper solution containing a mercury salt to provide ametal coating thereon, appl 'ng molten zinc to the coated casting, quenc 'ng the casting and ageing it at an elevated tern-'- perature not in excess of 165 C.

8. The method of treating malleable cast iron which comprises applying acopper coating to the iron, applying molten zinc to said 0 copper coating, quenching the casting and ageing it at a temperature. withinthe range. of 120 C. to 145 C. hours.

9. The method of treating malleable; cast iron which comprises ageing the casting at a temperature higher than 100 0.. but not for approximately 6 in excess of 540 (1., and then cooling in air.

approximately 36 hours.

12. The method of treating malleable cast iron which comprises ageing the casting at a temperature of approximately 300 C.

13. The method of restoring a brittle malleable casting to normal condition which comprises ageing the casting at a temperature within the range of 100 C. to 540 (1, and for a period of at least six hours.

14. The method of restoring a brittle mal-- leable casting to normal condition which comprises ageing the casting at a temperature within the range of 100 C. to 540 C.

15. The method of treating zinc coated malleable cast iron whichcomprises ageing the casting for a period of time varying .from 3.to 72 hours and at a temperature within the range of 100 C. to 165 C.

- 16. The method of treating malleable cast iron which comprises ageing the casting for a period of time varying from 3 to 72 hours and at a temperature within the range of 190 C. to 540 0.

In witness whereof, I have hereunto set my hand this 17th day of May, 1926. l

' IRVING R. VALENTINE.

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